1. Field of the Invention
The present invention relates to a coding method that is used when converting an information block that is sequentially extracted from an information sequence and that serves as a conversion unit into a code block. More particularly, the invention concerns a coding method that can realize the coding wherein D.C. components have been suppressed while suppressing the increase ratio of the code length to the original information bit length as much as possible, and a coding apparatus.
2. Related Art
Several coding methods that are used when converting an information sequence into a code sequence have hitherto been disclosed.
Among them, a CMI code (Coded Mark Inversion code) method is known as one example of the coding method that can realize the coding wherein D.C. components have been suppressed.
The CMI code method is a coding method wherein, as Illustrated in FIG. 1, each time "1" appears in the information sequence, coding thereof is performed by converting the level of a time slot corresponding to this "1" to a high level and a low level in such a way as to change over the level of the time slot alternately to these high level and low level while, on the other hand, each time "0" appears in the information sequence, coding thereof is performed by converting the level of a time slot corresponding to this "0" in such a way that the levels of the first half and the second half prepared by dividing this slot into two equal parts differ from each other.
According to this CMI code method, it is possible to realize the coding wherein D.C. components have been completely suppressed.
Also, as one example of the coding method that can suppress the increase ratio of the code length to the original information bit length as much as possible, there is known a mB1C code (m Binary with 1 Complement insertion code) method.
Among the mB1C code methods, for example, a 10B1C code method is the coding method wherein, as illustrated in FIG. 2, every 10-bit-length information block, an inverted code (P*) of the last information item (P) is added to the information block at a position after the information item (P), whereby coding of the 10-bit-length information block is performed by converting this 10-bit-length information block to a code block having a code length of 11.
According to this 10B1C code method, the increase ratio of the code length to the original information bit length is 1.1 times. Therefore, it is possible to realize the coding wherein this increase ratio has been suppressed as much as possible.
However, in the above-described coding method, there was involved therein the problem to be solved that it is difficult to realize the coding wherein D.C. components have been suppressed while suppressing the increase ratio of the code length to the original information bit length as much as possible.
Namely, according to the CMI code method, the coding wherein D.C components have been completely suppressed can be realized indeed. However, when viewing this code method from the standpoint of the increase ratio of the code length to the original information bit length, because this increase ratio inconveniently becomes twice higher, this code method is not preferable from this standpoint of suppressing the increase ratio.
Meanwhile, according to the 10B1C code method, the coding wherein the increase ratio of the code length to the original information bit length has been suppressed as much as possible can be realized indeed. However, when viewing this code method from the standpoint of the D.C. component suppression degree that is defined by the ratio of the number of the codes "1" contained in the code block to the total number (11) of the codes in the code block, because the range within which the code "1" can take its position is from "1" to 10 and the D.C. component suppression degree thereof changes within a range of from approximately 9% to approximately 91%, this code method is not preferable from the standpoint of D.C. component suppression.
Namely, the suppression of the increase ratio of the code length to the original information bit and the suppression of the D.C. components are mutually in a relationship of trade-off. Therefore, in the above-described conventional coding method, there was involved the problem to be solved that it is extremely difficult to realize the coding wherein D.C. components have been suppressed while suppressing the increase ratio of the code length to the original bit length as much as possible.
Under the above-described circumstances, there has been earnestly expected among the associated people the development of a novel coding method that can realize the coding wherein D.C. components have been suppressed while suppressing the increase ratio of the code length to the original bit length as much as possible.